Back reflection block for ultrasonic flaw detection

ABSTRACT

AN ULTRASONIC BACK REFLECTION BLOCK HAVING AN ENTRY SURFACE RECEIVING AN ULTRASONIC WAVE FROM A SURFACE OF A MATERIAL BEING TESTED, AND A BACK SURFACE REFLECTING THE ULTRASONIC WAVE IN SUBSTANTIALLY THE SAME DIRECTION AS IT IS RECEIVED FROM THE ENTRY SURFACE. TO CHECK RESOLVING POWER OF THE EQUIPMENT, AN &#34;ARTIFICIAL FLAW&#34; IS PROVIDED IN THE BLOCK, SUCH AS BY FORMING A GROOVE OR THE LIKE IN THE BACK SURFACE, TO CHANGE THE REFLECTION CHARACTERISTICS OF THE BLOCK.

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[ l l l l I l l Inventors Takashi Fuji;

Matsuo Sato, Yokohamashi, Japan Appl. No. 716,757 Filed Mar. 28, 1968 Patented June 28, 1971 Assignee Nippon Kokan Kabushiki Kaisha Priority Mar. 28, 1967 Japan 19013/67 BACK REFLECTION BLOCK FOR ULTRASONIC FLAW DETECTION 7 Claims, 16 Drawing Figs.

US. Cl 73/67.7 Int. Cl GOln 29/04 Field of Search 73/675,

Primary Examiner-James J. Gill Attorney-Robert D, Flynn ABSTRACT: An ultrasonic back reflection block having an entry surface receiving an ultrasonic wave from a surface of a material being tested, and a back surface reflecting the ultrasonjc wave in substantially the same direction as it is received from the entry surface. To check resolving power of the equipment, an artificial flaw" is provided in the block, such as by forming a groove or the like in the back surface, to change the reflection characteristics of the block.

PATENTEUJUN28I97I 3,587,300

' sum 1 OF 3 v Fig |A Fig IB Fig IC- T'akashi FUJI BACK REFLECTIGN BLOCK FOR ULTIKASONIC FLAW DETECTIGN The present invention relates to improvements in ultrasonic inspection methods to detect internal and surface flaws of metal products, and more particularly to ultrasonic back reflection blocks to make stable and accurate detection irrespective of the quality, size and surface of the products to be inspected, without using an ultrasonic reference block.

In the prior art, (such as disclosed in Journal of Metals, May I960, p. 392-). 397), the angle beam search method to detect discontinuities in a material has a wide range of applications such as inspection of the welds of metal plates, or laminations or surface discontinuities of tubes. in this prior art method, the result of detection is largely dependent upon the sensitivity of the transducer to the material. It has been, therefore, the standard practice to set up the sensitivity of a transducer by using an ultrasonic reference block. The block generally, according to the above-mentioned article in "Journal of Metals, consists of a metal block containing several kinds of holes of specified size and depth. Generally speaking, the sensitivity of ultrasonic wave pulse echo equipment is indicated in such a manner that the height of the echo may amount to about 50 of that of the initial pulse. However, there is much difficulty involved in attaining stable results even with the above known ultrasonic units preadjusted at proper sensitivity. This is because of (l) the difference of properties between the reference block used for setting up the sensitivity and the material tested in actual practice, and (2) the substantial difference in the surface characteristics between the reference block and the material being tested. Generally speaking, surface characteristics of the reference block are quite good so that the ultrasonic wave is traced through the block without any trouble, while the surface of the test material is often rough so that the ultrasonic wave encounters difficulty travelling through the article. If the properties of the test material are different from that of the reference block, the predetermined sensitivity is changed, resulting in the danger of overlooking or erroneously reading the magnitude of discontinuities or flaws in the material.

An object of the present invention is to provide an improved ultrasonic testing apparatus having good detecting characteristics for internal discontinuities in a variety of metal products, more particularly, in the weld of plates and tubings.

Another object of the present invention is to provide a stable ultrasonic angle beam searching method irrespective of the differences of properties and surface characteristics of the test material from those of the reference metal block.

Still another object of the present invention is to provide an improved ultrasonic testing apparatus which does not require use of a reference metal block. The sensitivity of the testing equipment is set up by directly operating on the metal product at starting of the actual testing.

A further object of the present invention is to provide an improved ultrasonic testing apparatus having a smaller sized back reflection block which has a pulse travelling through the metal product reflecting perpendicularly to the back surface of the above block.

The present invention allows the sensitivity to be set up by using an ultrasonic back reflection block instead of the reference metal block. The reflection echo is obtained by reflection from a flaw or reflection from the back surface of the reflection block.

The invention will now be described in detail in conjunction with the accompanying drawings in which:

FIGS. lA-IC are various ultrasonic blocks of the present invention;

FIG. 2A is a typical test set up illustrating the present invention in use;

FIG. 2B is the pulse pattern of an input pulse and a reflec tion echo as shown on a cathode ty tube screen;

FIG. 3A shows the present invention applied to flaw detection in a weld;

FIG. 3B shows the pulse patterns for the apparatus of FIG. 3A;

FIGS. 4A4D are side views of other embodiments of the present invention;

FIGS. 5A-5D, respectively are top views of the embodiments of FIGS. 4A-4D; and

FIG. 6 shows the pulse pattern of the input and reflection echos for the embodiment of FIG. 4A.

FIGS. lA-IC show various kinds of ultrasonic back reflection blocks 6, 7, 8, with respective entry surfaces 6|, 7|, 81 and respective back reflection surfaces 62, 72, 82. FIG. 2A illustrates one example of the back reflection block in practical use, wherein an ultrasonic transducer I0 is positioned at one surface of the material) being inspected. At a predetermined distance therefrom the ultrasonic back reflection block 6 is placed. An ultrasonic pulse from the transducer I0 travels through the material 9 at a fixed angle with respect to its entry surface. The ultrasonic pulse, as indicated by the broken line, bounces back and forth between the entry surface and back surface of the material 9 being inspected. A portion of the pulse is transmitted via the contact surface 61 into the ultrasonic back reflection block 6. The ultrasonic pulse travels to the back surface 62 of block 6, is reflected perpendicular to the back surface 62 and travels back again to the starting point ofthe initial pulse at surface 6|. The reflected ultrasonic pulse is then fed into a cathode-ray tube screen and is displayed on its screen. FIG. 28 represents one example of the display on said screen, showing the initial pulse II and the back reflection echo pulse 52.

The above is an experiment to explain the present inven tion. The actual practice for detection is explained as follows. FIG. 3A illustrates a material 9 to be inspected having a flaw 14 in a weld I3. A portion of the ultrasonic wave (or pulse) travelling through the article (shown as a broken line in FIG. 3A) is reflected from the flaw 14 before reaching the ultrasonic back reflection block 6 and is returned back to the transducer it). Therefore, the echo recorded on the cathoderay tube screen is higher than that reflected from the reflection face 62 of the ultrasonic back reflection block 6. FIG. 3B shows the relative height of these pulse echoes, designating 15 as the initial pulse, 16 as the flaw echo pulse of the weld and 17 as reflection echo pulse from the reflection face 62 of block 6. In this case, the sensitivity of the equipment is set up in such a manner that the reflection echo I7 is about half as high as the initial pulse 15.

As is apparent from the above description, according to the present invention, the above sensitivity is not set up by means of comparison with the reference metal block, but is preset for the individually inspected materials themselves, so that the sensitivity will not be affected by properties and surface characteristics of the inspected material. Further, in the present invention, the resolution characteristics for the detection equipment can be observed, simultaneously with the echos, of sensitivity. That is, as indicated in FIGS. 4A FIGS. 5A, the back reflection block 6 is provided with an artificial flow 63 on the reflection surface 62. The flaw 63 is a groove in this embodiment. The block 6 is fixed on the material 9 to be inspected as indicated in FIG. 2A. Then, the transducer I0 is moved in the horizontal direction of FIG. 2A, resulting in a pattern on the screen of the cathode-ray tube similar to the one shown in FIG. 6. This pattern results due to the fact that the back reflection rate is lower on the groove 63 (i.e. the artificial flaw). The deeper the incision in the wave form of the pattern of FIG. 6 becomes, that is, the larger the value of h,/h, (FIG. 6) becomes, the better resolution characteristics the equipment shows. Thus, according to the present invention, it is easy to observe the performance and to observe weakening of the detector to be used. Thus, the present invention is of high utility and quite effective compared with the conventional method making use of a convention reference metal block.

FIGS. SB-4C and 5B-5C show blocks having other types of artificial flaws. FIGS. 43 and 5B show a V-shaped groove 63, FIGS. 4C and SC show a groove 63 with a rough surface and FIGS. 4D and 5D show a hole 63 drilled through the block. These different blocks are used depending upon the particular application.

The present invention can fully achieve the expected objects with very small sized ultrasonic back reflection blocks. The above described block, which shows satisfactory results, is very small, the length being 40 mm. and the width being It! mm. As a practical matter. any back reflection block will be satisfactory if it has large enough entry and back reflection the speed of sound material longitudinal wave transverse wuve acrylite 2.720 m/sec. 14st) m/sec.

5.880 m/sec. 331i) m/sec.

mild steel According to the equation of sin 8,/ sin 6,=C,/ C, (C, and C, are the mean speed of sound within each material) regarding the refraction of a sound wave beam at the contact surface between the above-mentioned mild steel and acrylite, when 6, of mild steel is 70", the refraction angle 6, of acrylite will be 50 30'. FIGS. lA-lC illustrate examples of back reflection blocks made on the basis of the above calculation. The block must be made to have the sound wave beam reflecting perpendicular to the back reflection surface, irrespective of properties of the block. Therefore, if this condition is satisfied, the back reflection surface may be flat 62 as shown in FIG. 1A, curved 72 as shown in H0. 18, or spherical 82 as shown in FIG. [C With these blocks, the back reflection echos appear as a rectangle, a straight line and a spot, respectively. They have their own characteristics and are properly used according to the objects of the detection in particular cases. There is no need of any special contact medium between the reflection block and the inspected material at all. In actual detection equipment according to the present invention, water, machine oil, water glass, coating agent, liquid binding agent and others were experimented with, all of which showed good results with good stability.

As described in detail, the present invention provides an ultrasonic back reflection block of small size and light weight which is directly put on the material to be inspected. The blocks provide excellent resolution and sensitivity characteristics and is capable of stably and continuously inspecting material for flaws. The detection method was explained herein with reference to welded material, but it should be obvious that the present invention can be applied to all kinds of inspections, for example, for detecting internal discontinuities such as laminations, cracks, voids, or inclusions, and other flaws of plates, billets, bars, forgings, tubings, or the like.

We claim:

I. Ultrasonic flaw detection apparatus wherein ultrasonic waves are introduced into a test' material and reflections of said waves are received from the material including an ultrasonic back reflection block having an entry surface for receiving an ultrasonic wave from a surface of the material being tested; a back surface receiving the ultrasonic wave from the entry surface of said block, said back surface being shaped and oriented to reflect the ultrasonic wave in substantially the same direction as it is received from said entry surface back into said material toward the point where the waves are introduced into said material; and an artificial flaw formed in said block for changing the back reflection characteristics of said block, to enable the resolving power ofsaid flaw detection apparatus to be examined.

2. Apparatus according to claim I wherein said artificial flaw is fonned in the back surface of said block.

3. Apparatus according to claim 2 wherein said artificial flaw includes a groove formed in said back surface. I

4. Apparatus according to claim 2 wherein said artificial flaw includes a groove having a circular cross section formed in said back surface.

5. Apparatus according to claim 2 wherein said artificial flaw includes a V-shaped groove formed in said back surface.

6. Apparatus according to claim 2 wherein said artificial flaw includes a groove having a corrugated surface formed in said back surface.

7. Apparatus according to claim 1 wherein said artificial 

